1. Field of the Invention
The present invention relates to an apparatus for recording and reproducing a television signal (e.g. composite video signal or luminance signal and carrier color signal) and, more particularly, to a recording/ reproducing apparatus such as a video tape recorder (hereinafter referred to as VTR) of color-under recording type with conversion of a carrier color signal into a lower frequency band.
2. Description of the Prior Art
In the known home VTRs currently available for recording and reproducing composite video signal of NTSC system, there is adopted a color-under recording type which converts a carrier color signal into a lower frequency band.
According to such technique, a composite video signal of NTSC system is separated into a luminance signal (Y signal) and a carrier color signal (C signal) frequency-multiplexed in a higher frequency range of 3 to 4 MHz of the luminance signal, and then the carrier color signal (hereinafter referred to simply as color signal) is frequency-converted to a band lower than 1 MHz. Meanwhile, the luminance signal is limited to a band of 2 to 3 MHz and is frequency-modulated to become an FM luminance signal. Subsequently the FM signal thus obtained and the lower-frequency converted color signal are frequency-multiplexed and recorded on a recording medium such as a magnetic tape.
And in a playback mode, the frequency-multiplexed FM luminance signal and lower-frequency converted color signal are separated into individual signals through a high pass filter (HPF) and a low pass filter (LPF). Then, out of the signals thus separated, the FM luminance signal is frequency-demodulated while the lower-frequency converted color signal is inversely converted in such a manner that the color subcarrier frequency is restored to the former frequency. And the color signal is frequency-multiplexed to the higher frequency range of the luminance signal again to resume the original composite video signal.
In such recording technique with conversion of the carrier color signal into a lower-frequency band, the recent trend of employing some improved recording media such as metal tape has made it possible to raise the FM carrier of the FM luminance signal up to a frequency band of 2 MHz or so which is higher than the frequency conventionally used, hence realizing a wide-band recording home VTR to ensure a high resolution of the reproduced picture.
Relative to the conventional VTR signal processing techniques, there are known the following U.S. Patents filed by the present applicant (Hitachi, Ltd.).
U.S. Pat. No. 4,524,380 PA1 U.S. Pat. No. 4,613,912 PA1 U.S. Pat. No. 4,612,585 PA1 U.S. Pat. No. 4,607,293 PA1 U.S. Pat. No. 4,672,468 PA1 U.S. Pat. No. 4,677,486 PA1 U.S. Ser. No. 91,452 (Aug. 1987) now U.S. Pat. No. 4,825,299) PA1 U.S. Ser. No. 113,603 (Oct. 1987) (now U.S. Pat. No. 4,786,986)
In addition to the above, the pending patents are as follows.
In the conventional home VTR, it is customary in a playback mode that, as mentioned, the luminance signal obtained by frequency demodulation and the color signal obtained by inverse frequency conversion are frequency-multiplexed again to resume the original composite video signal.
FIGS. 7A and 7B graphically represent a comparison of the frequency bands, in a pre-recording state and a post-playback state, of a luminance signal and a color signal contained in the composite video signal obtained by a conventional home VTR.
In FIGS. 7A and 7B, Y and C denote a luminance signal and a color signal respectively, and the frequency is taken along the abscissa.
In the pre-recording composite video signal, as shown in FIG. 7A, the frequency band of the luminance signal is lapped over that of the color signal. However, according to the conventional home VTR where the recordable band width for the luminance signal is as narrow as 2 to 3 MHz, the frequency band of the luminance signal is not lapped over the frequency band of the color signal, as shown in FIG. 7B. Accordingly, even if the separation of the composite video signal into the luminance signal and the color signal is incomplete in the recording mode (for example, when the luminance signal is recorded out of the composite video signal limited to a band width of 3 MHz or so by a LPF), it is extremely rare that, in case the post-playback composite video signal is separated again into the luminance signal and the color signal, the color signal component leaks into the separated luminance signal.
However, in the conventional wide-band recording home VTR mentioned above, the band width adapted for recording the luminance signal is extendable to about 4 MHz, so that in the post-playback composite video signal, the frequency band of the luminance signal is extended as indicated by a broken line in FIG. 7B and is thereby lapped over the frequency band of the color signal. Consequently, if the separation of the composite video signal into the luminance signal and the color signal is incomplete in the recording mode, there occurs an undesired phenomenon that, when the post-playback composite video signal is separated again into the luminance signal and the color signal, most of the color signal component leaks into the separated luminance signal. Furthermore, in the playback by the VTR, the luminance signal and the color signal do not exactly satisfy the requirement of frequency interleave relationship due to some time-base variation, so that even with the use of a comb filter for achieving accurate separation into the luminance signal and the color signal, it is still impossible to eliminate leakage of the color signal component into the luminance signal. As a result, in the conventional wide-band recording home VTR, some interference is caused by the harmful influence of the color signal component having leaked into the luminance signal, thereby raising a problem of deterioration in the image quality of the reproduced picture.
Besides the above, in the conventional wide-band recording home VTR where the luminance signal is recorded after frequency modulation as mentioned, triangular noise is increased in accordance with widening of the frequency band to consequently bring about another problem of deterioration in the signal-to-noise ratio with regard to the reproduced signal.